The present invention relates to a mobile telephone system and, more particularly, to vehicle-mounted or on-board telephone equipment which serves as a mobile station in a mobile telephone system.
A mobile telephone system has on-board telephone equipment mounted on individual vehicles to serve as mobile stations, base stations each being assigned to a different service area for interchanging information with on-board equipment existing in the service area, a control station for supervising a plurality of base stations, and a mobile telephone switching station interconnecting the control station and a switched telephone network.
To hold a communication with desired on-board telephone equipment on an ordinary telephone set, a control station supervising a particular base station which offers a service area where the desired equipment exists is called by a telephone network to which the ordinary telephone set is interconnected, via a mobile telephone switching station. In response, the control station calls the desired on-board equipment via the base station.
On the other hand, to originate a call on the on-board equipment, the control station is called via the particular base station offering the service area where the on-board equipment exists. In response, the control station assigns message channels to the service area to allow the on-board equipment to hold a communication.
A problem with the mobile communication system is that when no idle channels are available due to the increase in the amount of communications, no communications can be held, i.e., a communication is allowed only when any of the channels having been occupied becomes idle. It has been customary, therefore, to repetitively send a call request until an idle channel has been seized.